Low cost peripheral devices, such as floppy disk drives, for personal computers can be enhanced in performance by the use of equalizer circuits in their read/write channels. The typical adaptive magnitude equalizer circuit is very expensive and would exceed the cost of the floppy disk drive the equalizer would be used in.
In the past, adaptive magnitude equalizers have been implemented with tapped delay lines and digital-to-analog converters. While such devices work well, they are very expensive.
Examples of patents showing various implementations of magnitude equalizers utilizing a tapped delay line include U.S. Pat. Nos. 3,750,026, 3,875,333 and 3,978,435. Adaptive equalizers of this type have used digital-to-analog converters (DAC's) or spectrum analyzers to make them adaptive. In all cases, these are very expensive equalizers. The cost of the DAC or the spectrum analyzer eliminates these equalizers from use in low-cost peripheral devices.
An alternative design is shown by W. Rupprecht, "A Hybrid Adaptive Equalizer System for High Speed Digital Transmission," IEEE International Symposium on Circuits and Systems Proceedings, (New York 1980) pp. 580-584. Rupprecht uses phase shifting filters in place of tapped delay lines. A microcomputer generates the weighting factors used in the equalizer to make it adaptive. The speed of the microcomputer is too slow for many adaptive equalizer applications and definitely too slow for high speed data storage devices.